When a plant is infected by a pathogen, several defence mechanisms are induced in planta. A rapid production of reactive oxygen species (ROS) released into the apoplast, is one of the earliest responses to pathogen infection. We investigated the possible role of these antioxidants in Pyrus communis 'Conference' after infection with Erwinia amylovora. We analysed expression of the genes for SOD, APX and CAT and their diverse isoforms with Real Time qPCR. Infected and mock infected leaves, but also young and old leaves were included. In this study, we noticed a significant difference in transcription levels of some isoforms between mock and infected leaves en between young and old leaves. These differences could partially account for the different progression rates by which a young and aged leaf get infected.